This application claims the priority of European Patent Application, Serial No. 011 17 242.6, filed Jul. 17, 2001, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a bumper for a motor vehicle, and in particular to a bumper of a type having a cross member for attachment to longitudinal members of a vehicle chassis, wherein the cross member has a shell element, which extends over a major part of the length of the cross member.
Bumpers are arranged across the front and rear of a motor vehicle between the plastic casing, forming an end piece of the body, and the chassis of the motor vehicle, and are provided to prevent damage in the event of a low speed impact. Oftentimes, impact absorbers, so called crash boxes, are disposed between the cross member and the longitudinal members, to absorb the energy in the event of a collision by converting the impact energy into deformation work.
German Pat. No. DE 44 13 641 C1 describes a bumper which is provided with a cross member to form an energy absorber. The cross member has a split configuration and includes a C-shaped rear part for attachment to the vehicle body and a flat end panel which covers the rear part. Arranged at the front side of the cross member is an impact body in the form of a solid profile spanning over the length of the cross member and made of a material, e.g. plastic foam or a honeycomb structure of plastic, intended to absorb energy.
German Pat. No. 196 43 049 A1 describes a bumper having a cross member in the form of a hollow profile composed of two U-shaped profiled shells. Disposed in the shells are reinforcing inlays which are provided in the neutral fiber with lateral slits. In addition, angled reinforcement strips are arranged at the attachment points.
Reinforcements integrated in the cross member are capable to limit damage in the event of a collision at slight speed. Tests have shown that, for example, at an impact speed of 4 km/h against a pendulum or a barrier, the reinforcements protect the cross member and the vehicle from damage. The demand on reinforcements is in particular high when U.S. automobiles are concerned. An established test, commonly called pole crash test, has been developed in which an automobile is pulled at a speed of 8 km/h backwards against a pole. The determined damage is evaluated and used in concert with other tests to assess the discount category for insurance purposes.
It would be desirable and advantageous to, provide an improved bumper with increased stiffness and strength to limit damage in particular when used as rear bumper.
According to one aspect of the present invention, a bumper includes a cross member for attachment to longitudinal members of a vehicle chassis, wherein the cross member has a shell element spanning over a major part of the length of the cross member, wherein the shell element has incorporated therein at least one deep-drawn reinforcement member of cup shaped configuration.
According to another feature of the present invention, the reinforcement member may be made of sheet steel. Production can be carried out on a large scale in an economical and cost-efficient manner. The cross member and the components of the reinforcement member may be fabricated in separate operations. Subsequently, the components of the reinforcement member are positioned in the cross member and joined thereto. The geometric configuration of the reinforcement member can be best suited to the cross member at hand as far as moment of resistance as well as strength behavior and stiffness behavior are concerned. Depending on the demand on motor vehicles, it is, of course, possible to integrate several reinforcement members in suitable locations. For convenience and sake of simplicity, much of the following description will be made in relation to one reinforcement member. Of course, it will be understood that the principles described in the following description with respect to one reinforcement member are equally applicable to the arrangement of more than one reinforcement member.
The geometry of reinforcement member may vary. Oval, round or rectangular cylindrical cross sections are conceivable. The reinforcement member may be partially integrated in the cross member and enables a targeted configuration to suit the stiffness behavior and strength behavior as well as bending pattern during impact. The stress behavior can be suited through coordination of number, geometry and position of reinforcement members.
The reinforcement member effects in concert with the cross member shell a doubling of the wall thickness and an increase of the wall thickness at critical locations of the bumpers so that bumpers in their entirety can be fabricated in a targeted manner to take into account expected force patterns in case of stress through impact or collision.
According to another feature of the present invention, the shell element may include a central web having opposite end faces, and two legs, with one leg extending from one end face of the web and the other leg extending from the other end face of the web, wherein the reinforcement member has an end wall configured to complement and to contact the web of the shell element. Suitably, the reinforcement member can be joined, e.g. welded, with the web to the inside of the shell. The reinforcement member may partially or fully contact the web. Practice has shown that a complete flat engagement of the end face of the reinforcement member upon the web is currently preferred. The contours of mutually contacting surfaces should be suited to one another.
According to another feature of the present invention, the shell element has flanges, and the reinforcement member is provided with a collar for attachment to the flanges. The attachment may be realized through spot welding or seam welding. Of course, other joining techniques, such as gluing or clinching, are also conceivable. Suitably, the flanges are directed inwardly toward the shell body.
According to another feature of the present invention, the reinforcement member may be heat-treated (quenching and tempering). This is especially advantageous when exposed to high stress and during crash like in a pole crash test.
The local attachment of the reinforcement member leads in a pole crash test to a reduction of the penetration depth of the pole in the event of impact. The bumper according to the present invention includes a configuration of the cross member that meets stress demands and functional demands. A diverting of the forces from the cross member to the impact absorber/crash boxes is ensured. As a consequence, damage is diminished and possible repair costs are reduced. Moreover, the weight of the cross member can be reduced. As the reinforcement member builds up resistance, the wall thickness of other components of the bumper assembly may be decreased. This may also have a positive effect on the overall weight. Furthermore, the reinforcement member assumes the function of an end panel for the shell-shaped cross member so as to the legs of the shell element are prevent from opening or spreading apart to the outside in the event of a collision.